Hard disk storage devices include at least one rotating magnetic disk and a magnetic head that reads and writes data along concentric tracks on the disk. Some storage devices include a stack of multiple disks to increase storage capacity. Continuing growth in the demand for disk storage capacity may be met by increasing the number of disks in a stack. However, increasing the number of stacked disks increases the volume needed to package the storage device, and in many applications the volume available for the disk storage device is severely constrained.
One of the factors that affects the volume of the packaging is the height of the disk stack. In addition to the number and thickness of the disks in the stack, the height of the stack is affected by the configuration of the mechanism used to position the magnetic heads used to read and write data on the disks. Generally, a magnetic head is mounted to a movable arm by means of a flexible member. The arm is positioned so that the magnetic head is located adjacent to the surface of the disk. The arm is moved to position the head to read or write data on different concentric tracks of the disk. In some configurations, the head may move in a linear path across the disk surface. In one linear configuration, multiple heads which are displaced along the direction of travel are used to provide access to the entire surface of a disk without the necessity of moving a single head across all of the tracks of the disk. In other configurations, the arm is rotatably mounted, causing the head to move in an arcuate path across the disk surface.
In multiple disk configurations where both sides of each disk are being accessed, it is necessary to position at least two heads, each facing a disk surface, in the gap between the opposed disk faces of adjacent disks. This gap, or disk spacing, is an important factor in determining the overall height of the drive. Various configurations have been used to position heads in the gap. In one configuration, two heads are mounted on a single arm with one head directly above another such that each head traces the same arcuate path. In several different known configurations, two cantilevered arms are used, each attached to a single head. One such configuration employs two interleaved arms. Another employs a pair of arms which are located side by side. A further configuration employs a pair of arms positioned at an acute angle to each other.